Determine the least value of declination of stars so that stars can be seen?

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    Declination Stars Value
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Discussion Overview

The discussion revolves around determining the least value of declination for stars to be visible from a specific location on Earth. It includes considerations of celestial coordinates and their implications for star visibility based on geographic position.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that stars must be above the horizon to be observed and questions how to determine the least declination for visibility.
  • Another participant explains that from the equator, all stars are visible, but as one moves northward, the visibility of stars with negative declination decreases, eventually becoming permanently invisible at the North Pole.
  • A later post inquires whether it is possible to find the declination and right ascension of a star on a future date given its coordinates on a certain day.
  • Another participant responds that declination and right ascension are fixed celestial coordinates for practical purposes, although they can change over long periods due to proper motions and precession.

Areas of Agreement / Disagreement

Participants generally agree on the fixed nature of declination and right ascension for short-term observations, but there is no consensus on the implications of declination for visibility based on geographic location, as the discussion includes varying perspectives on visibility limits.

Contextual Notes

The discussion does not resolve the complexities of how declination affects visibility based on specific geographic locations, nor does it address the long-term changes in celestial coordinates in detail.

nicolauslamsiu
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For stars to be observed in a certain place, the stars must be at a position above the horizon. Yet, how to determine the least value of declination of stars so that stars can be seen?
 
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Imagine that you are observing from a point on the equator. All stars are visible at some time of the year, having any declination from +90º to -90º. Now, imagine you move your observatory 20º to the North. The South celestial pole will also dip by 20º below your horizon, and with it, all the stars having a declination more negative than -70º... If you continue moving your observatory to the North, you will reach the North pole, from which any star with a negative declination is permanently below the horizon, and can't be observed.

I believe that this description is better than a formula...
 
ok...get it...one more question:
the declination and R.A. of a star on a certain day is given.
is it possible to find the declination and right ascension of a star some days after?
 
Both declination and right ascension are fixed celestial coordinates, and they don't change in days... In the long term, they do, because of proper motions and the precession of the equinoxes, but -for normal use- they can be considered as fixed.
 

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